So, the house I’m in has a separate poolhouse (for a pool that the previous owners never got around to installing). The poolhouse is enclosed and waiting to be finished. I would like to make it into a home office.
It already has some electricity:
Two 20A 120V circuits feed off from a breaker panel in the basement of the house, through buried PVC 3/4" conduit, and into the poolhouse. The wires used: four 12 AWG THHN 600V wires, plus a fifth ground wire.
Once it gets into the poolhouse, the conduit terminates in a metal 4-outlet box. One circuit supplies those 4 outlets. The other circuit is spliced to romex cable in the box and then routed out through the studs to a 2-outlet box and another 4-outlet box.
So that’s what I have.
Here’s what I’d like to do:
install a subpanel in the poolhouse (already own the new subpanel)
power a 240V 2000W 8.3A electric baseboard heater (already own the heater) from a dedicated circuit on the new subpanel
power two switched overhead can lights from a dedicated circuit on the new subpanel
power one or two additional circuits to supply wall outlets (for computer equipment)
My big problem, then is this: I need to supply sufficient power to the subpanel to accomplish the above, but I really, really don’t want to have to feed new wire/cable through the buried conduit; it’s (a) crowded and (b) going to be a pain to do, with the various turns.
Can I accomplish what I need with the existing 12 AWG wires? Or do I need to yank them out and feed through new cable?
I’m not sure how crowded it is, but if you have enough space to pull the old wires out, you could tape the new wires to the old old ones and when you pull the old ones through it would feed the new ones as it goes.
I am not an electrician, so don’t put too much legitimacy into what I’m saying. But if you have four 12-AWG wires, couldn’t you use two for the 240 VAC circuit, and two for the 120 VAC circuit? Just use a 240 VAC / 20 A double-pole breaker for the 240 VAC circuit (if they make such a thing - most are 30 A to 50 A), and a 120 VAC / 20 A breaker for the 120 VAC circuit. And then use the ground wire to ground everything.
But again, I am not a licensed electrician, and I know nothing about the NEC. The only thing I see that might be illegal is using one ground wire for both circuits.
Electric heaters were required to be on a circuit that used only 80% of a wire’s capacity last time I looked. You also can not locate any electric outlet over them anymore. The highest amperage you can run on 12 AWG wire is 20amps. Your electrical code may require a 15amp limit on the 12 AWG wire. A run of too long a distance can also limit you to only 15amps. You have about 10amps of capacity for each of the two 120V opposite phased circuits, if the main line is 20amps. A feed line that can only be fed 15amps will give you only 5amps for each of the two opposite phased 120v circuits. You must have a four wire line running to the breaker box. One for each hot terminal, one for the neutral terminal, and one for the ground terminal. You have to have a neutral and a ground for safety and code compliance, and the neutral can’t be uninsulated.
Sounds like a fun project.
I’m guessing you have a red, a black, two white wires and a green in that PVC?
The extra white wire isn’t really needed, but that won’t matter. The guy that wired the shed could have used a common white as long as the other two wires aren’t on the same phase in the panel.
Re-using the same wires;
You will have to install a 20 amp double pole breaker in the basement panel. The red and the black will terminate on that breaker and one of the whites will go to the ground bar along with the green. The other white will be a spare wire.
Install the subpanel and wire the branch circuits accordingly.
A two pole 15 amp breaker for the heater, a single pole 15 for the lights and another single pole 15 for the computer outlets. 3 breakers, four spaces, done.
What I would do;
Install a double pole 50 amp breaker in basement panel.
Pull out all the number 12’s except the green one. Use the green wire as a pull wire for three #8’s (three black wires with one taped white on the ends for the nuetral) and a #10 ground. You can get 6 #8’s in a 3/4 conduit so pulling 3 #8’s and a 10 should be a piece of cake. As you probably guessed #8 is good for 50 amps.
When you install the wires in the subpanel you have to keep the grounds and the nuetrals seperate. There needs to be a ground bar and a nuetral bar and the nuetral bar should NOT be bonded to the subpanel as it is in the main panel (in the main panel the bonding point for all the grounding electrodes in essentially the same point, but not in sub panels). There are exceptions if the outbuilding is more that X feet from the main building but I’m assuming it’s within 75 feet or so, correct?
That’s all I’ve got for now, time is up. I’ll check back tomorrow for any further Q’s.
Is the PVC conduit Rigid Schedule 80, Schedule 40 and HDPE, Type A, or Type EB.
Each is listed separately under Annex C of the 2005 NEC. From there, the insulation of the conductors must be determined and checked for number of conductors permitted. Insulation rating also bears consideration.
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